If you want to do a bunch of calculations and work on them with e.g Excel, I recommend NASA JPL's Horizon's Program. http://ssd.jpl.nasa.gov/horizons.cgi. It is free, has a nice web interface and computes just about anything astronomical that you might want (although you have to deduce the EoT from the Apparent Solar Time). Results are downloadable directly to your computer either as text or .csv files. It is of course JPL who maintain the basic DE405 routines that are used by just about all other professional programs.
The other great program is US Naval Observatory's MICA program available on disk for a few dollars. MICA uses DE405 as its ultimate engine. Anyone who wants to use Meeus's routines, I have the whole lot as a callable Excel macro function Best regards Kevin Karney On 20 Dec 2010, at 16:38, Bill Gottesman wrote: > Hello Sundial-listers, > > I used to rely on Luke Coletti's Great Circle website's GROK calculator for a > precise calculation of sun positions, but that page has been non-operative > for about a year now. > > The National Renewable Energy Laboratory (NREL) in Golden Colorado has > provided an excellent resource at http://www.nrel.gov/midc/solpos/spa.html, > similar to GROK. Their MIDC Sun Position Algorithm utilizes Jean Meeus' > modified VSOP87 algorithm, reportedly accurate to 0.0003 degrees between > years -2000 to +6000. The NREL site also provides a link to an explanation > of this algorithm as a pdf file http://www.nrel.gov/docs/fy08osti/34302.pdf. > > The program will output a table of sun positions over a range of dates, in as > little as 1 second intervals. It allows many options for sun position > measurements, but the most helpful to me are topocentric azimuth, geocentric > sun declination, Topocentric (uncorrected) sun elevation, and topocentric sun > elevation corrected for atmospheric refraction. These tables are essential > to me in the field when I delineate true north using a theodolite, and lay > out predictive sightings for sunrise and sunset. > > Beware; if you select "Topocentric Zenith Angle", the results are corrected > for refraction, though they do not tell you this up front. You must select > "Topocentric (uncorrected) sun elevation" if you want to exclude atmospheric > refraction. > > Lastly, they report the time of sunrise/sunset as when the center of the sun > is 0.8333 degrees below the horizon (uncorrected for refraction). This is to > account for the width of the sun, and an average effect of refraction, and > represents the moment that the advancing or receding limb of the sun (not the > sun's center) crests the horizon. > > -Bill > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial >
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